Marine Mammal Species Likely to Be Encountered in the Coastal Waters of Virginia from Analysis of Stranding Data
Total Page：16
File Type：pdf, Size：1020Kb
VAQF Scientific Report # 2014-07a Prepared for the Virginia Department of Mines, Minerals and Energy Marine Mammal Species likely to be Encountered in the Coastal Waters of Virginia from Analysis of Stranding Data Submitted by: Susan Barco and W. Mark Swingle Virginia Aquarium & Marine Science Center Foundation VAQF Scientific Report 2014-07a Introduction There have been no consistent, year-round marine mammal surveys of the ocean waters off of Virginia since the late 1970s (Scott et al. 1979). Data on marine mammal presence and seasonality are needed to inform state and federal agencies responsible for permitting offshore energy development and construction. A long term data set of marine mammal presence exists in the stranding record. Marine mammals often wash ashore sick, injured or dead and records of these stranding events can serve as a proxy of animal presence when no other data exist. Stranding data cannot provide information on species absence since an animal must strand in order to be counted, and deep water, offshore species rarely strand even though they may be plentiful. These data can, however, minimally provide a list of species to consider for survey efforts and, for more common and coastal species, suggest seasonal presence. Stranded marine mammals in Virginia The Virginia Aquarium & Marine Science Center Foundation (VAQF) Stranding Response Program has a database of marine mammal strandings in Virginia dating to 1988. In an earlier assessment, Potter (1991) documented a summary of the historical records of marine mammals from Virginia strandings. From these two sources, 32 different marine mammal species have stranded in Virginia: four pinniped species; 27 cetacean species, including four endangered species; and one endangered sirenian species (Table 1). Although none have stranded in Virginia, sighting data also indicate the seasonal and likely presence of Killer whales (Orcinus orca) and other species such as the false killer whale (Pseudorca crassidens) and blue whale (Balaenoptera musculus) in the region (Cummings et al. 2014, Potter 1991, VAQF Stranding Database 2014 - unpublished). Stranding records range from over 1,800 bottlenose dolphins (Tursiops truncatus) to a single stranding of a Sowerby’s beaked whale (Mesoplodon bidens). The endangered species were primarily baleen whales and included humpback whales (Megaptera novaeangliae), fin whales (Balaenoptera physalus), sei whales (Balaenoptera borealis) and critically endangered northern right whales (Eubalaena glacialis). The endangered Florida manatee has stranded in Virginia and is regularly sighted on an annual basis. Two of the five most numerous marine mammal species in the stranding record were pinnipeds, harbor seals (Phoca vitulina) and harp seals (Pagophilus groenlandica). While healthy harbor seals are occurring in increasing numbers in Virginia and strand relatively rarely, most harp seals in Virginia, an ice seal species, are undernourished or sick weanlings and are therefore counted almost exclusively in the stranding record. This demonstrates one of the drawbacks of relying solely on stranding data for species presence. These data should therefore be used as a guide for developing survey designs. The other three species that most commonly stranded were bottlenose dolphin (Tursiops truncatus), harbor porpoise (Phocoena phocoena) and common dolphin (Delphinus delphis). These five species and the four endangered whale species are discussed in greater detail below. 1 VAQF Scientific Report 2014-07a Table 1: Marine mammal species in stranding records from Virginia (ESA= listed under the U.S. Endangered Species Act). Location and seasonality data are included for species listed in bold. ‘Historic’ refers to published accounts of the species. For these species, no animals were in the Virginia stranding record from 1988-2013. Common Name Scientific Name ESA Strandings Baleen whales Bryde's whale Balaanoptera brydei Y historic fin whale Balaenoptera physalus Y 11 humpback whale Megaptera novaeangliae Y 33 minke whale Balaenoptera acutorostrata N 9 northern right whale Eubalaena glacialis Y 4 sei whale Balaenoptera borealis Y 2 Delphinids Atlantic spotted dolphin Stenella frontalis N 4 Atlantic white-sided dolphin Lagenorhynchus acutus N 14 bottlenose dolphin Tursiops truncatus N 1,593 Clymene dolphin Stenella clymene N C. Potter pers. comm common dolphin Delphinus delphis N 98 long-finned pilot whale Globicephala melas N 14 melon headed whale Peponocephala electra N 2 pantropical spotted dolphin Stenella attenuata N historic pygmy killer whale Feresa attenuata N 3 Risso's dolphin Grampus griseus N 22 rough toothed dolphin Steno bredanensis N 14 short-finned pilot whale Globicephala macrorhynchus N 7 striped dolphin Stenella coeruleoalba N 16 Other toothed whales Cuvier's beaked whale Ziphius cavirostris N historic dwarf sperm whale Kogia sima N 10 Gervais' beaked whale Mesoplodon europaeus N 6 harbor porpoise Phocoena phocoena N 318 pygmy sperm whale Kogia breviceps N 24 Sowerby's beaked whale Mesoplodon bidens N 2 sperm whale Physeter macrocephalus N 1 True's beaked whale Mesoplodon mirus N 1 Pinnipeds grey seal Halichoerus grypus N 15 harbor seal Phoca vitulina N 82 harp seal Pagophilus groenlandica N 38 hooded seal Cystophora cristata N 12 Sirenians Florida manatee Trichechus manatus Y annual sightings 2 VAQF Scientific Report 2014-07a Endangered species The northern right whale (Eubalaena glacialis) is critically endangered under the U.S. Endangered Species Act, and there are estimated to be 444 individuals in the northwest Atlantic (Waring et al. 2013). Northern right whales are a slow moving, coastal species that is susceptible to both vessel strikes and gear entanglements. Northern right whales spend the warm water months in high latitude waters feeding on copepods. In the fall, some individuals disperse from feeding areas in New England and Atlantic Canada. Breeding females travel to ocean waters off the Georgia/Florida border to calve. The winter distribution of non-breeding females, adult males and juvenile whales is unknown, but whales may move extensively between feeding and breeding areas. The mid-Atlantic region is part of the migratory corridor between summer feeding areas and winter breeding areas and may also be a destination for non-breeding individuals. Since 1988, there have been four right whale strandings in Virginia, all since 2001 (Figure 1). Three of the strandings occurred in winter (Jan-Mar) and one in late summer (Jul-Sep; Figure 2). All strandings were on ocean facing beaches suggesting that the animals were in ocean habitat. The whales ranged in size from 7.7-16.0 m. Three were adult females, one pregnant with a full term fetus, and one was a male calf. The calf and the pregnant female had injuries consistent with ship strike. One whale most likely died from injuries caused by entangling line and the cause of death for the fourth animal could not be determined due to decomposition of the carcass. 6 5 4 3 3 2 1 Number strandingsof 1 0 0 0 winter spring summer fall Figure 2: Seasonality of Northern right whale strandings in Virginia from 1988-2013 (winter=Jan-Mar; spring=Apr-Jun; summer=Jul- Sep; fall=Oct-Dec). Figure 1: Location of northern right whale strandings in Virginia from 1988-2013. 3 VAQF Scientific Report 2014-07a Humpback whales (Megaptera novaeangliae) are the endangered species that stranded most often in Virginia with 33 animals reported since 1988. There are five stocks described based on feeding ground distribution. The Gulf of Maine stock of humpback whales is estimated to include 823 individuals (Waring et al. 2013), but humpbacks that stranded or were observed live in the mid-Atlantic have been identified to three different stocks: primarily the Gulf of Maine stock, but also the Gulf of St. Lawrence and Newfoundland stocks (Barco et al. 2002). Humpbacks stranded primarily on ocean facing beaches but also stranded in Chesapeake Bay (Figure 3). Humpback strandings have occurred in all seasons (Figure 4) and in all months except December and January. Stranded humpback whales in Virginia ranged in size from 6.4 to 15.4 m, with most being juveniles (Figure 5). For 22 of the 33 strandings, we could assess the whale for signs human interaction. Two of the animals had no signs of human interaction, eleven had marks consistent with entanglement and nine had wounds consistent with vessel strike. 20 15 13 10 9 6 5 5 Number strandingsof 0 winter spring summer fall Figure 4: Seasonality of humpback whale strandings in Virginia from 1988-2013 (winter=Jan-Mar; spring=Apr-Jun; summer=Jul- Sep; fall=Oct-Dec). 20 15 13 10 4 5 1 2 2 2 0 Number strandingsof Length (cm) Figure 3: Location of humpback whale strandings in Virginia from Figure 5: Length of stranded humpback whales in 1988 -2013. Virginia from 1988-2013. Length was only available for 24 animals. 4 VAQF Scientific Report 2014-07a Fin whales (Balaenoptera physalis) are the second largest whale species after blue whales and are listed as endangered in the U.S. The North Atlantic population is considered to be a single population (stock) and the best available estimate of abundance is 3,522 whales from 2007 (Waring et al. 2013). Fin whales are most commonly found from Cape Hatteras northward and spend the warmer months feeding in high latitude waters. It has been suggested that calving takes place in the fall and winter offshore of the U.S. mid-Atlantic but no concrete evidence of overwintering exists (Waring et al. 2013). Vessel strike is the most common cause of stranding for fin whales. Of the eleven fin whales that stranded in Virginia since 1988, we were able to conduct a human interaction evaluation on five animals. All five had evidence of vessel strike and one also had entanglement marks. We were able to collect a total length on seven carcasses and they ranged in size from 8.0-17.9 m. There were three males and five females identified. Unlike humpback whale strandings, fin whale strandings occurred primarily in winter with one stranding each in spring and summer.